P690QL2 steel plate with ultrahigh die welding and low-temperature performance and manufacturing method of P690QL2 steel plate

Abstract

The invention relates to a P690QL2 steel plate with ultrahigh die welding and low-temperature performance and a manufacturing method of the P690QL2 steel plate. The P690QL2 steel plate comprises the following chemical components in percentage by weight: 0.04%-0.12% of C, 0.02%-0.08% of Si, 1.0%-1.2% of Mn, 1.5%-2.5% of Ni, 0.3%-0.7% of Cr, 0.7%-0.9% of Mo, 0.07%-0.12% of V, 0.02%-0.04% of Ti, less than or equal to 0.002% of S, less than or equal to 0.002% of P, 0.03%-0.06% of Als and the balance of Fe and inevitable impurity elements. The steel plate is applied to the liquid cargo tank of the LCO2 transport ship, has high strength and low-temperature toughness requirements, is easy to weld and has ultrahigh die welding performance, the V-type impact energy of the steel plate at-60 DEG C is larger than or equal to 150 J, the CTOD at-55 DEG C is larger than 0.2 mm, and the machining and welding use requirements of pressure-bearing equipment are met.

Description

Technical Field

[0001] The present invention belongs to the field of manufacturing low-temperature steel plates for liquid cargo tanks of liquefied carbon dioxide transport ships, and in particular relates to a P690QL2 steel plate with ultra-high die welding and low-temperature performance and a manufacturing method thereof. Background Art

[0002] Currently, liquid and supercritical fluid carbon dioxide transportation is becoming a means of long-distance storage and acquisition, and carbon dioxide transport ships can meet the diversified transportation needs of liquid carbon dioxide.

[0003] The cryogenic storage tanks of LCO2 transport ships require P690QL2 steel to have not only high strength and toughness, but also high low-temperature toughness and easy welding. Compared with normalized steel, the mold welding performance of the steel plate obtained by the quenching and tempering heat treatment process is difficult to control.

[0004] In the prior art, CN115786820 discloses a method for manufacturing P690QL2 marine tank steel. This method enhances the strength and low-temperature toughness of the steel plate by adding alloying elements such as Nb, V, Ti, Cr, and Mo. Through TMCP and quenching and tempering, the resulting marine tank steel plate has a toughness of approximately 200 J and a lath bainite structure. Despite this, while Examples 1-3 meet the low-temperature toughness requirements for P690QL2 steel, the low TMCP production efficiency and the close dependence of the steel plate's red-hot temperature on the amount of water applied make it difficult to ensure uniform microstructure and properties during production. Furthermore, the TMCP process for thin-gauge steel plate produces a poorly contoured plate. Patent document CN 117418158 discloses an ultra-low carbon equivalent P690QL2 steel plate for hydrogen storage vessels and its manufacturing method. This plate is also produced using the TMCP process, resulting in a finished plate thickness of 40-80mm. However, according to the design and construction requirements for LCO2 carriers, the minimum thickness of low-temperature steel plate for liquid cargo tanks in LCO2 carriers is far less than 40mm, failing to meet application requirements. Patent document CN 115852120 discloses a method for producing P690QL2 steel plate with a thickness of ≤50mm. This plate is also produced using the TMCP process. The plate's CTOD value at -35°C was tested, but it does not meet application requirements based on the design and construction requirements for LCO2 carriers.

[0005] The paper on P690QL2 low-temperature steel also studies its rolling process, heat treatment process, microstructure, etc., striving to better meet the technical requirements of P690QL2 steel in EN10028-6, but cannot meet the latest requirements. Summary of the Invention

[0006] The present invention aims to provide a P690QL2 steel plate with ultra-high die welding and low-temperature performance and a manufacturing method thereof. The steel plate is used in liquid cargo tanks of LCO2 transport ships, has high strength and low-temperature toughness requirements, is easy to weld, and has ultra-high die welding performance. The steel plate of the present invention has a -60°C V-type impact energy of ≥150J and a -55°C CTOD of >0.2mm, meeting the processing and welding requirements of pressure-bearing equipment.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A P690QL2 steel plate with ultra-high die welding and low-temperature performance, wherein the chemical composition of the steel is as follows by weight: C: 0.04%-0.12%, Si: 0.02%-0.08%, Mn: 1.0%-1.2%, Ni: 1.5%-2.5%, Cr: 0.3%-0.7%, Mo: 0.7%-0.9%, V: 0.07%-0.12%, Ti: 0.02%-0.04%, S: ≤0.002%, P: ≤0.002%, Als: 0.03%-0.06%, and the balance is Fe and unavoidable impurity elements.

[0009] The reasons for limiting the composition of the P690QL2 steel of the present invention are as follows:

[0010] Carbon (C) in this invention acts as an interstitial solid solution strengthening element to enhance the strength and hardness of this low-temperature steel. The limiting solubility of C in steel decreases with increasing Cr content. Excessive C content can reduce the toughness of the steel and hinder welding. Therefore, this invention selects a C content of 0.04% to 0.12%.

[0011] Silicon: Silicon not only increases steel strength but also serves as a reducing and deoxidizing agent. A Si content exceeding 2% significantly promotes ferrite coarsening, reducing the steel's ductility and toughness. Excessive Si content also negatively impacts the steel's weldability. Therefore, the present invention limits the Si content to 0.02% to 0.08%.

[0012] Manganese: Mn is a strong austenite-stabilizing element and an effective element for increasing steel strength. It is infinitely miscible with Fe. However, adding too much Mn to steel can coarsen the grains, increase the carbon equivalent, and thus affect the steel's weldability, and can also cause temper brittleness. Therefore, the present invention selects a Mn content of 1.0% to 1.2%.

[0013] Nickel: Nickel is an effective element that can make steel obtain excellent strength and low-temperature toughness. The lattice constant of Ni is close to that of γ-Fe. It is one of the elements that infinitely expand the austenite zone and can increase the stability of austenite. Therefore, after quenching and tempering treatment, nickel-containing steel can obtain a completely refined tempered bainite structure, and the strength and toughness of the steel are well matched. However, nickel is a scarce resource and is expensive, so the Ni content is controlled at 1.5% to 2.5%.

[0014] Sulfur: Sulfur easily forms FeS and MnS inclusions in steel, causing hot brittleness and significantly reducing the toughness of the steel. Therefore, the sulfur content in the steel should be reduced as much as possible.

[0015] Phosphorus: P often segregates at grain boundaries in steel, destroying the continuity of the matrix, significantly reducing the toughness of the steel, deteriorating the welding performance, and easily causing cold brittleness. Therefore, the P content in the steel should be reduced as much as possible.

[0016] Molybdenum: Mo produces second-phase particles during tempering, improving the steel's strength and creep resistance, particularly maintaining structural stability at medium and high temperatures. Mo also refines grain size and reduces brittleness in the heat-affected zone of welds. However, excessive Mo content can lead to embrittlement of the steel. Therefore, the present invention sets the Mo content range to 0.7% to 0.9%.

[0017] Chromium: Cr is a strong carbide-forming element. It forms stable carbides with C in steel, which play a role in strength at room temperature and high temperature. In order to ensure that this steel has sufficient strength, the Cr content range of the present invention is set at 0.3% to 0.7%.

[0018] Aluminum: Aluminum primarily acts as a nitrogen fixator and deoxidizer. AlN, formed by the combination of Al and N, effectively refines grains. However, excessive AlN content impairs steel toughness and can easily cause cracks in ingots and steel sheets. Therefore, the AlN content is controlled within a range of 0.03% to 0.06%.

[0019] Vanadium and titanium: V and Ti primarily contribute to grain refinement. They inhibit austenite deformation and recrystallization during hot working, preventing grain growth. They also provide precipitation strengthening through the strain-induced precipitation of their carbonitrides. Ti also immobilizes sulfur and nitrogen, increasing the steel's strength. V reduces the brittleness of the weld heat-affected zone and improves the steel's weldability. Therefore, the present invention limits the V content to 0.07% to 0.12% and the Ti content to 0.02% to 0.04%.

[0020] The thickness of the steel plate is 5 to 60 mm.

[0021] The yield strength of the steel plate is ≥690MPa, the tensile strength is 770~940MPa, and the elongation is ≥17%.

[0022] The steel plate has a -60°C V-type impact energy of ≥150J and a -55°C CTOD of >0.2mm.

[0023] A method for manufacturing a P690QL2 steel plate with ultra-high die welding and low-temperature performance includes smelting, continuous casting, heating, rolling, quenching heat treatment, tempering heat treatment and die welding heat treatment. The specific method includes:

[0024] 1) The smelting process utilizes a converter (BOF) + LF + VD refining process. The LF furnace produces reducing slag for desulfurization, inclusion reduction, and composition adjustment. A complete set of dephosphorization and rephosphorization control technologies is employed for high-phosphorus hot metal to produce ultra-low-phosphorus steel billets. The molten steel is then degassed in a VD vacuum furnace, ensuring a holding time of 15-20 minutes. H and O contents are measured to ensure [H] ≤ 1.3 ppm and [O] ≤ 14 ppm.

[0025] 2) The continuous casting: the casting is protected throughout the whole process, the secondary oxidation during the continuous casting process is reduced, the inclusion content in the steel is reduced, and the purity of the steel is improved to ensure that the center segregation of the ingot is not higher than level B0.5; the slab slow cooling and shot blasting: after the continuous casting ingot with a cross-sectional size of 250 to 300 mm comes off the line, it is stacked in a slow cooling pit for slow cooling, so that the gas in the ingot is fully diffused and discharged, and the gas content of the ingot is reduced to the greatest extent. The slow cooling time is ≥48 hours, and the surface of the ingot is cleaned by shot blasting.

[0026] 3) Heating: The ingot is fed into a walking beam furnace at an average heating rate of 8 to 10 min / cm. To ensure high-temperature rolling, it is heated to 1255 to 1300°C. When the core temperature reaches the surface temperature, it is kept warm for at least 1.5 hours to allow the alloying elements in the steel to fully dissolve and ensure the uniformity of the composition and properties of the final product.

[0027] 4) Rolling: High-pressure water is used to remove iron oxide scale before rolling. The steel ingots undergo two-stage controlled rolling. After finishing rolling, each of the three passes has a reduction of ≥20%. The first stage rolling temperature is 980-1020°C, the second stage rolling temperature is 880-920°C, and the final rolling temperature is 520-880°C. During the first stage rolling in the recrystallization zone above 980°C, recrystallization and deformation are alternated to fully refine the austenite grains. Rolling in the non-recrystallization zone at approximately 850°C increases the effective nucleation area of ferrite and refines the ferrite grains.

[0028] 5) Quenching heat treatment: After rolling, the steel plate is subjected to offline quenching treatment. The alloying elements Cr, Mn, Ni and other elements in the steel can increase the hardenability of the thick plate. The ferrite-austenite equilibrium phase transformation starting temperature A of the steel of the present invention is measured. C1 The ferrite-austenite equilibrium transformation end temperature is 603℃. C3 is 872℃, and the quenching temperature is A C3+(50~100℃), the preferred quenching temperature is 925~945℃, and the holding time is 2~5min / mm, the purpose is to make the organization uniformly austenitized while the austenite grain size is uniform, each alloy element is fully diffused, and ensure that the austenite grains are not too large.

[0029] 6) The tempering heat treatment: After quenching, the steel plate is subjected to a tempering process at a tempering temperature of 350-450°C and a holding time of 2-3 min / mm; medium-temperature tempering is selected with a shortened holding time. The purpose of medium-temperature tempering is to obtain a tempered troostite structure of lath ferrite and fine-grained cementite.

[0030] 7) Die welding heat treatment: The heat-treated steel plate is subjected to die welding heat treatment at 500-600°C for 180-360 minutes. The purpose is to simulate the changes in the microstructure and properties of the steel plate during the welding process and thus determine whether the welding process affects the performance of the steel plate.

[0031] In the present invention, the smelting of P690QL2 low-temperature steel for the liquid cargo tank of the LCO2 transport ship adopts converter + LF + VD refining, which ensures the precise control of harmful elements and gas content in the steel; the continuous casting process protects the pouring and slow cooling of the slab throughout the process, which ensures the internal quality of the casting; the controlled rolling ensures the refinement of the initial structure; and the post-rolling heat treatment adopts a quenching + tempering process to fully ensure the strength and low-temperature toughness of the steel plate.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The present invention adopts a complete set of dephosphorization and controlled rephosphorization technology, combined with the precipitation strengthening of Mo second phase particles during the tempering process and the fine grain strengthening of V and Ti, to improve the low temperature toughness and -55℃ CTOD performance of the steel plate in the heat treated and die welded state.

[0034] (2) The P690QL2 low-temperature steel plate for LCO2 transport ships manufactured using this technical solution is combined with trace alloying elements to control the morphology and quantity of the second-phase particles precipitated, thereby improving the strength of the steel plate. The finished product has a thickness of 5 to 60 mm, and its heat-treated and die-welded properties all achieve a yield strength of ≥690 MPa, a tensile strength of 770 to 940 MPa, an elongation of ≥17%, a -60°C V-type impact energy of ≥150 J, and a -55°C CTOD of >0.2 mm.

[0035] (3) The present invention uses 250-300 cross-section continuous casting billets to produce P690QL2, with the aim of ensuring the compositional uniformity of the billets, while ensuring that the compression ratio of the subsequently rolled steel plate is not less than 5, ensuring that the grain structure before heat treatment, i.e., in the hot-rolled state, is not coarse, and providing fine-grained structure inheritance for the subsequent heat treatment structure.

[0036] (4) The present invention adopts a series of measures such as spraying treatment on the upper and lower surfaces of the ingot, controlling heating during the heating process, high-pressure water descaling, and high-temperature rolling to ensure that the steel plate has good surface quality.

[0037] (5) The present invention is achieved by C3 The quenching treatment is carried out at a temperature 50-100℃ above the tempered temperature to ensure the effective precipitation of alloy elements in the steel plate, increase the ferrite content in the tempered bainite structure, improve the toughness of the steel plate, and at the same time make the various alloy elements fully diffuse and ensure that the austenite grains are not too large.

[0038] (6) The present invention is achieved by c1 Tempering treatment is carried out in the following medium temperature zone. The addition of strong carbide-forming elements V and Mo slows down the dissolution of alloy cementite, increases the diffusion activation energy of carbon in the α phase, and slows down the diffusion of carbon in the α phase. In order to ensure the effective precipitation of alloy elements in the steel plate while taking into account the post-die welding performance of the steel plate, an appropriate medium temperature tempering temperature is set to improve the toughness of the steel plate.

[0039] (7) The present invention performs die welding heat treatment by keeping the temperature at 550℃±50℃ for 180 to 360 minutes, and controls and controls the performance of the steel plate after welding by continuously precipitating second phase particles through tempering of the Mo alloy element in the high temperature section and the fine grain strengthening effect of V. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the microstructure of the steel plate manufactured in Example 1 under an optical microscope. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the specific implementation methods of the present invention are further described below in conjunction with examples. The following examples are used to specifically illustrate the contents of the present invention. These examples are only general descriptions of the contents of the present invention and do not limit the contents of the present invention.

[0042] The present invention provides a P690QL2 low-temperature steel plate containing alloy components such as Ni, Cr, Mo, V, and Ti, which is produced using a two-stage controlled rolling process combined with a quenching and tempering heat treatment process. The plate exhibits ultra-high die weldability and low-temperature performance for liquid cargo tanks of LCO2 carriers. Addressing existing technical deficiencies in P690QL2 production, the present invention utilizes a novel composition design for the new P690QL2 steel plate with a thickness of 5 to 60 mm. The steel is produced using a continuous casting process to produce continuously cast ingots with a cross-section of 250 to 300 mm. The ingots are then hot-rolled and subsequently quenched and tempered at high temperatures to achieve P690QL2 steel plates with excellent strength-toughness matching, ultra-high die weldability, and a -55°C CTOD performance. Sandblasting is also employed to ensure the surface quality of the new P690QL2 steel plates with a thickness of 5 to 60 mm.

[0043] The following examples are only some of the best implementation schemes of the present invention and do not limit the scope of the aforementioned invention and technical means. The production process of P690QL2 low-temperature steel plate for liquid cargo tanks of LCO2 transport ships of the present invention is as follows: molten iron pretreatment - converter smelting - refining outside the furnace (LF+VD) - continuous casting - stacking and slow cooling - surface treatment of ingot - heating - rolling - flaw detection - heat treatment - packaging and warehousing. Table 1 shows the components involved in each example, Table 2 shows the heating, rolling and cooling processes of the slab in the example, Table 3 shows the heat treatment process of the example, Table 4 shows the comprehensive mechanical properties of the example in the heat-treated state, Table 5 shows the die-welded heat treatment process of the example, and Table 6 shows the comprehensive mechanical properties of the example in the die-welded state.

[0044] Example 1:

[0045] The smelting process was conducted in a 100-ton top-blown oxygen converter. Carbon and temperature were coordinated during the blowing process to ensure that P and S contents met internal control requirements. Desulfurization was performed in the LF furnace to reduce inclusions and adjust the composition. The VD furnace maintained pressure for 17 minutes. H and O contents were measured, and [H] = 1.2 ppm and [O] = 12 ppm.

[0046] The continuous casting process is fully protected during casting, and the billet size is 250mm; the slab is slowly cooled in the slow cooling pit, and the surface of the billet is shot blasted after slow cooling; after the billet is removed from the furnace, it is descaled by high-pressure water and then subjected to two-stage controlled rolling of rough rolling and finishing rolling; and then heat treatment is carried out. The steel plate manufactured according to the scheme of this embodiment is corroded by 4% nitric acid alcohol solution and the structure under an optical microscope is shown as follows: Figure 1 , the microstructure of the steel plate is tempered bainite + ferrite.

[0047] Example 2:

[0048] The smelting process was conducted in a 100-ton top-blown oxygen converter. Carbon and temperature were coordinated during the blowing process to ensure that P and S contents met internal control requirements. Desulfurization was performed in the LF furnace to reduce inclusions and adjust the composition. The VD furnace maintained pressure for 18 minutes. H and O contents were measured, and [H] = 1.1 ppm and [O] = 13 ppm.

[0049] The continuous casting process is fully protected, and the billet specification is 300mm; the slab is slowly cooled in a slow cooling pit, and the surface of the billet is shot blasted after slow cooling; after the billet is removed from the furnace, it is descaled with high-pressure water and then subjected to two-stage controlled rolling of rough rolling + finishing rolling; followed by heat treatment.

[0050] Example 3:

[0051] The smelting process was conducted in a 100-ton top-blown oxygen converter. Carbon and temperature were coordinated during the blowing process to ensure that P and S contents met internal control requirements. Desulfurization was performed in the LF furnace to reduce inclusions and adjust the composition. The VD furnace held pressure for 19 minutes. H and O contents were measured, and [H] = 1.2 ppm and [O] = 10 ppm.

[0052] The continuous casting process is fully protected, and the billet specification is 250mm; the slab is slowly cooled in a slow cooling pit, and the surface of the billet is shot blasted after slow cooling; after the billet is removed from the furnace, it is descaled with high-pressure water and then subjected to two-stage controlled rolling of rough rolling + finishing rolling; followed by heat treatment.

[0053] Example 4:

[0054] The smelting process was conducted in a 100-ton top-blown oxygen converter. Carbon and temperature were coordinated during the blowing process to ensure that P and S contents met internal control requirements. Desulfurization was performed in the LF furnace to reduce inclusions and adjust the composition. The VD furnace maintained pressure for 16 minutes. H and O contents were measured, and [H] = 1.3 ppm and [O] = 14 ppm.

[0055] The continuous casting process is fully protected, and the billet specification is 300mm; the slab is slowly cooled in a slow cooling pit, and the surface of the billet is shot blasted after slow cooling; after the billet is removed from the furnace, it is descaled with high-pressure water and then subjected to two-stage controlled rolling of rough rolling + finishing rolling; followed by heat treatment.

[0056] Example 5:

[0057] The smelting process was conducted in a 100-ton top-blown oxygen converter. Carbon and temperature were coordinated during the blowing process to ensure that P and S contents met internal control requirements. Desulfurization was performed in the LF furnace to reduce inclusions and adjust the composition. The VD furnace maintained a pressure hold time of 20 minutes. H and O contents were measured, and [H] = 1.3 ppm and [O] = 12 ppm.

[0058] The continuous casting process is fully protected, and the billet specification is 250mm; the slab is slowly cooled in a slow cooling pit, and the surface of the billet is shot blasted after slow cooling; after the billet is removed from the furnace, it is descaled with high-pressure water and then subjected to two-stage controlled rolling of rough rolling + finishing rolling; followed by heat treatment.

[0059] Example 6:

[0060] The smelting process was conducted in a 100-ton top-blown oxygen converter. Carbon and temperature were coordinated during the blowing process to ensure that P and S contents met internal control requirements. Desulfurization was performed in the LF furnace to reduce inclusions and adjust the composition. The VD furnace maintained a pressure hold time of 15 minutes. H and O contents were measured, and [H] = 1.2 ppm and [O] = 10 ppm.

[0061] The continuous casting process is fully protected, and the billet specification is 250mm; the slab is slowly cooled in a slow cooling pit, and the surface of the billet is shot blasted after slow cooling; after the billet is removed from the furnace, it is descaled with high-pressure water and then subjected to two-stage controlled rolling of rough rolling + finishing rolling; followed by heat treatment.

[0062] Example 7:

[0063] The smelting process was conducted in a 100-ton top-blown oxygen converter. Carbon and temperature were coordinated during the blowing process to ensure that P and S contents met internal control requirements. Desulfurization of the reducing slag in the LF furnace was used to reduce inclusions and adjust the composition. The VD furnace's holding time was 17 minutes. H and O contents were measured, and [H] = 1.2 ppm and [O] = 14 ppm.

[0064] The continuous casting process is fully protected during pouring, and the billet specification is 300mm; the slab is slow-cooled in a slow cooling pit for 58 hours, and the surface of the billet is shot blasted after slow cooling; after the billet is removed from the furnace, it is descaled with high-pressure water and then subjected to two-stage controlled rolling of rough rolling + finishing rolling; followed by heat treatment.

[0065] Example 8:

[0066] The smelting process was conducted in a 100-ton top-blown oxygen converter. Carbon and temperature were coordinated during the blowing process to ensure that P and S contents met internal control requirements. Desulfurization was performed in the LF furnace to reduce inclusions and adjust the composition. The VD furnace held pressure for 19 minutes. H and O contents were measured, and found to be [H] = 1.1 ppm and [O] = 13 ppm.

[0067] The continuous casting process is fully protected, and the billet specification is 300mm; the slab is slowly cooled in a slow cooling pit, and the surface of the billet is shot blasted after slow cooling; after the billet is removed from the furnace, it is descaled with high-pressure water and then subjected to two-stage controlled rolling of rough rolling + finishing rolling; followed by heat treatment.

[0068] Table 1 Chemical composition of the present invention (wt%)

[0069] C Si Mn P S Ni Cr Mo V Ti Als Example 1 0.05 0.05 1.03 0.0019 0.0014 1.92 0.37 0.78 0.12 0.021 0.052 Example 2 0.08 0.03 1.12 0.0014 0.0008 1.5 0.54 0.81 0.08 0.038 0.06 Example 3 0.12 0.08 1.19 0.0012 0.0009 2.27 0.69 0.86 0.07 0.029 0.043 Example 4 0.04 0.02 1.06 0.0011 0.0016 2.48 0.43 0.87 0.09 0.033 0.032 Example 5 0.09 0.03 1.15 0.002 0.0017 1.97 0.7 0.9 0.1 0.025 0.03 Example 6 0.07 0.06 1 0.0016 0.0013 1.84 0.57 0.7 0.08 0.04 0.049 Example 7 0.11 0.08 1.09 0.0018 0.0019 2.18 0.7 0.77 0.09 0.02 0.058 Example 8 0.06 0.07 1.2 0.0015 0.0016 2.5 0.67 0.75 0.11 0.037 0.037

[0070] Table 2 Example slab heating, rolling and cooling processes

[0071]

[0072] Table 3 Example heat treatment process

[0073]

[0074] Table 4 Comprehensive mechanical properties of heat-treated steel plates

[0075]

[0076]

[0077] Table 5 Example mold welding heat treatment process

[0078]

[0079] Table 6 Comprehensive mechanical properties of die-welded steel plates

[0080]

Claims

1. A P690QL2 steel plate with ultra-high die welding and low temperature performance, characterized in that: The chemical composition of the steel by weight percentage is: C: 0.04%~0.12%, Si: 0.02%~0.08%, Mn: 1.0%~1.2%, Ni: 1.5%~2.5%, Cr: 0.3%~0.7%, Mo: 0.7%~0.9%, V: 0.07%~0.12%, Ti: 0.02%~0.04%, S: ≤0.002%, P: ≤0.002%, Als: 0.03%~0.06%, and the balance is Fe and unavoidable impurity elements.

2. The P690QL2 steel plate with ultra-high mold welding and low temperature performance according to claim 1, characterized in that: The thickness of the steel plate is 5 to 60 mm.

3. The P690QL2 steel plate with ultra-high mold welding and low temperature performance according to claim 1, characterized in that: The yield strength of the steel plate is ≥690MPa, the tensile strength is 770~940MPa, and the elongation is ≥17%.

4. The P690QL2 steel plate with ultra-high mold welding and low temperature performance according to claim 1, characterized in that: The steel plate has a -60°C V-type impact energy of ≥150J and a -55°C CTOD of >0.2mm.

5. A method for manufacturing a P690QL2 steel plate having ultra-high mold welding and low temperature performance according to any one of claims 1 to 4, characterized in that: Including smelting, continuous casting, heating, rolling, quenching heat treatment, tempering heat treatment and die welding heat treatment, the specific methods include: The tempering heat treatment: the tempering temperature is 350-450°C, and the holding time is 2-3 min / mm; The die welding heat treatment is carried out at 500-600° C. and kept warm for 180-360 minutes.

6. The method for manufacturing a P690QL2 steel plate with ultra-high mold welding and low temperature performance according to claim 5, characterized in that: The smelting adopts converter+LF+VD refining, wherein the pressure holding time of the VD furnace is 15 to 20 minutes.

7. The method for manufacturing a P690QL2 steel plate with ultra-high mold welding and low temperature performance according to claim 5, characterized in that: After the continuous casting billet comes off the line, it is stacked in a slow cooling pit for slow cooling, and the slow cooling time is ≥48 hours.

8. The method for manufacturing a P690QL2 steel plate with ultra-high mold welding and low temperature performance according to claim 5, characterized in that: The heating is carried out by heating to 1255-1300° C. and keeping the temperature for not less than 1.5 hours.

9. The method for manufacturing a P690QL2 steel plate with ultra-high mold welding and low temperature performance according to claim 5, characterized in that: The rolling process is as follows: the steel billet is rolled in two stages, the first stage rolling temperature is 980-1020°C, the second stage rolling temperature is 880-920°C, and the final rolling temperature is 520-880°C.

10. The method for manufacturing a P690QL2 steel plate with ultra-high mold welding and low temperature performance according to claim 5, characterized in that: The quenching heat treatment: the quenching temperature is 925-945° C., and the holding time is 2-5 min / mm.

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